In Vista and 7, there are two modes for Windows Task Manager.

One is large mode, which takes up a big footprint in performance.
The other is small mode, which takes up a small footprint in performance.

Press CTRL+Shift+Esc or right click on the Taskbar and click Task Manager (Start Task Manager in 7).

First, this is large mode (normal) in Task Manager:


By double-clicking on the inset border, (not the Aero shadowed border, but the inside border), you can change to small mode. It can be changed back either way. By selecting a tab at the top in large mode, you can then double-click the inset border and see only that tab, while turning the other tabs "off" to lower the footprint on performance. To go back to large mode, simply click the inset border again, and you return. See below for small mode.